Soil naturally radiates microwaves, and NASA’s Aquarius sensor aboard a satellite can detect the microwave signals that vary with changes in the wetness of the soil. Blue indicates highest levels of soil moisture while yellow are the lowest.

„Why is soil moisture important in the global climate system?

Soil moisture is crucial for plant growth. It is also a source of water for evapotranspiration. Because the evaporation of soil moisture requires energy, soil moisture has strong impacts on the surface temperature. Through controlling the exchange of water, energy and carbon fluxes between the land surface and the atmosphere, it plays important roles in various processes and feedback loops within the Earth system. Specifically, the soil moisture influences agricultural and hydrological processes, drought development, runoff generation and many other processes. Due to its importance for climate system, the soil moisture has been recognized as one of the Essential Climate Variables by the Global Climate Observing System.”… zum vollständigen Interview (Englisch)